Friends grow apart after a tragic accident claims one of their number. Years later, the dead girl appears to them to ask for their help in crossing over to the afterlife.

Kiyosumi's affection for his schoolmate Hari grows after he saves her from bullying, but a dark secret she's unwilling to share threatens their bond.

To solve the country's low birthrate problem, the Japanese government set up Otona Kōkō (Adult High School). Adults over 30 with no sexual experience are forcibly enrolled into Otona Kōkō by the government. Eito Arakawa is a 30-year-old single man. He graduated from a prestigious university and works at a bank. He has received recognition for his work there. He is also physically attractive, but he has never had sex. One day, he receives an entrance guide to Otona Kōkō.

Sanako Moriwaka (Mikako Tabe) is single and works in the accounting department of a soap company. For her job, she checks receipts and bills. Each slip that she reviews, mentions only the dollar amount and a brief reason for the expense. When Sanako Moriwaka reviews the slips, she can often discern suspicious facts surrounding the expense or even troubles in the lives of the employee.

A high school girl, Sayaka Kudō was the bottom of the class. After a year, she improved her deviation value from 30 to 70, then passed Keio University that is considered one of the most difficult to enter in Japan.